This invention relates to the stabilization of organic material normally tending to deteriorate. In particular, the invention relates to the protection of synthetic polymers against the harmful degradative effects, such as discoloration and embrittlement caused by exposure to light, especially ultraviolet light.
It is known that actinic radiation, particularly in the near ultraviolet region, has a deleterious effect on both the appearance and properties of organic polymers. For example, normally colorless or light colored polyesters yellow on exposure to sunlight as do such cellulosics as cellulose acetate. Polystyrene discolors and cracks, with accompanying loss of its desirable physical properties when exposed to actinic light, while vinyl resins, such as polyvinyl chloride and polyvinyl acetate spot and degrade. The rate of air oxidation of polyolefins such as polyethylene and polypropylene is materially accelerated by ultraviolet light.
It has been proposed to stabilize polymeric materials against ultraviolet light deterioration by the use of various types of ultraviolet absorbers. Thus U.S. Pat. No. 3,004,896 discloses for this purpose 2(2-hydroxyphenyl) benzotriazole derivatives, while U.S. Pat. No. 3,189,630 discloses certain metal salts of hydroxybenzoic acids which are useful as actinic stabilizers in synthetic polymers.
Additionally, in U.S. Pat. No. 3,120,540 there is discussed the reaction of substituted 4-piperidinol compounds with acid anhydrides having the formula ##STR2## where n is 1 to 4, to yield bis(polymethyl)-4-piperidinol alkanoates. In the example of this patent the probable formation of ##STR3## is mentioned as an intermediate in the synthesis of the bis(hydrogen sulfate)salt of bis(1,2,2,6,6-pentamethyl-4-piperidyl)succinate. The compounds of U.S. Pat. No. 3,120,540 are taught to possess significant pharmacological activity in lowering blood pressure. We have now found that certain acid half esters of hindered piperidines stabilize organic substrates against the degradative effect of ultraviolet light and that the degree of stabilization achieved is significantly greater in the case of higher acid half esters than in the case of the above-mentioned succinic acid half-ester. We have also found that certain hetero-atom containing piperidine half-esters and salts of piperidine half-esters are useful as stabilizers of organic materials.